/Engine/Source/Editor/UnrealEd/Public/FileHelpers.h
Unloads the specified package potentially containing an inactive world. When returning false, OutErrorMessage is supplied with a display string describing the reason why the world could not be unloaded.
static bool AttemptUnloadInactiveWorldPackage ( [UPackage](API\Runtime\CoreUObject\UObject\UPackage) * PackageToUnload, [FText](API\Runtime\Core\Internationalization\FText) & OutErrorMessage )